1. Field of the Invention
The present invention relates to an improved adhesive composition which can be quickly hardened under exposing to air and has high impact strength. More particularly, it relates to an adhesive composition which minimizes the toxicity caused by inhalation in the handling of the adhesive composition and imparts high adhesive strength to a wood and a metal and can be hardened for several to several tens minutes of the time for imparting enough strength for handling.
2. Description of the Prior Art
Anaerobic adhesive compositions (the bending operation should be conducted without contacting it with air) comprising a polyacryl type monomer and an anaerobic monomer have been known as the adhesive composition comprising an acryl type monomer.
The anaerobic adhesive compositions comprising a monomer whose polymerization is easily inhibited with oxygen in air, can be stored at room temperature even though a peroxide as a polymerization initiator is added to the adhesive composition because of the inhibition of polymerization with oxygen in air.
The anaerobic adhesive composition can be used by hardening it under air-tightening between adhered metal substrates or by hardening it by contacting it on a surface coated with a hardening accelerator.
In both cases, the edge part of the adhesive composition exposed to air is not hardened. Accordingly, the unhardened part of the adhesive composition should be taken off by a complicated operation such as to wipe out with a solvent after the hardening. When the operation for taking out the unhardened part is omitted, various disadvantages on the appearance of product and the environmental hygiene such as the adhesion on hand and cloth, the dust adhesion or the smell have been caused.
When the adhesive composition is easily exposed to air in the form of the adhered substrates such as the space of the adhered substrates is wide, or the adhered substrate is paper, cloth or a cut surface of wood or a foamed substrate e.g. sponge, the fatal disadvantages of unhardening and remarkably low adhesive strength which leads to inferior adhesion are caused. Accordingly, the kinds of the adhered substrates are quite limited, disadvantageously.
It has been known to combine an acryl ester monomer having less anaerobic property and an elastomer for imparting enough impact strength to prepare adhesive compositions.
In the polychloroprene type adhesive compositions of U.S. Pat. No. 2,981,650, the oxidizing agent for the redox catalyst was mixed, at the time of application, with the solution of the reducing agent for the redox catalyst and the polychloroprene and the liquid monomer having unsaturated double bond, whereby the hardening was attained.
In the case of U.S. Pat. No. 3,333,025, the peroxide was mixed, at the time of application, with the system prepared by adding the reducing agent for the redox catalyst to a syrup produced by partially polymerizing the liquid monomer having unsaturated double bond in the presence of polychloroprene etc. whereby the hardening was attained.
In the cases of the above-mentioned adhesive compositions, it has been taken a long period for hardening the adhesive compositions and it has been usual to measure the adhesive strength, 24 hours after the application.
Recently, the needs of the increase of the hardening speed and the improvement of processibility for a bonding operation have been increased and are indispensable factors for preventing the smell and the environmental pollution caused by vaporized components in the condition of unhardening for a long period, and for applying it to an automatic lines for the bonding operation.
It has been known to add methacrylic acid to the polychloroprene-vinyl monomer system as disclosed in U.S. Pat. No. 3,725,504 in order to improve the set time.
The impact strength has been low because of the polychloroprene-vinyl monomer partial polymer.
It has been known to add a peroxide to the adhesive composition comprising an elastomer of butadiene and the other monomer, a methacrylic acid ester monomer, methacrylic acid and a reducing agent for a redox catalyst to attain the hardening in U.S. Pat. No. 3,832,274.
However, in the adhesive composition comprising the main components of the methacryl type monomers which have relatively low anaerobic property, the stability in the storage of the adhesive composition is remarkably decreased by the addition of the peroxide as the oxidizing agent for the redox catalyst, to the monomer solution. Accordingly, it has been usual to mix the peroxide, at the time for application, with the adhesive composition containing a reducing agent for a redox catalyst in the conventional technology.
It has been disclosed to use the peroxides dissolved in a plasticizer such as dioctyl phthalate in U.S. Pat. No. 2,894,932, U.S. Pat. No. 2,981,650, U.S. Pat. No. 3,321,351 and U.S. Pat. No. 3,333,025.
It has been also known to use the composition of a glass-like organic polymer, an initiator catalyst and a solvent as an under-coat in Japanese Unexamined Patent Publication No. 47,425/1974.
It has been known to add a peroxide for the redox catalyst to the composition containing ethylenically unsaturated monomer as the methyl methacrylate composition containing benzoyl peroxide in U.S. Pat. No. 3,321,351. However, these compositions are not stable in the storage and are not to be practically used. (Japanese Unexamined Patent Publication No. 47425/1974).
When methacryl acid is used at high content such as 5 wt. % to 20 wt. %, the corrosion of metal is disadvantageously caused as the cases of U.S. Pat. No. 3,725,504 and U.S. Pat. No. 3,832,274. When methacrylic acid is contacted on a metal surface or is vaporized, the corrosion of the metal is easily caused, especially the corrosion of copper material used in an electrical apparatus which leads to disconnect a copper wire etc., whereby a serious failure is caused.
In Japanese Unexamined Patent Publication No. 97051/1974, it has been disclosed the fact that when an unsaturated organic acid is contained and the adhered product is exposed in severe environmental condition, rapid deterioration is caused.
Moreover, on the handling of an adhesive composition, when the adhesive composition is adhered on a skin of hand and foot, an inflammation of the skin may cause. Accordingly, the presence of methacrylic acid in the adhesive composition is not advantageous in the bonding operation.